The present invention relates to an apparatus for optically recording a screen, for example a scintillator screen, in several individual images, which are then combined into an overall image, as occurs, for example, in digital radioscopy in the quality control of products.
The technical field of application of the invention described here advantageously comprises processing X-ray image data, in particular in industrial quality control of products which is performed by means of X-radiation. An important case of application is the detection of shrink holes, porosities or other blemishes in castings such as aluminum wheels. Since the imaging area of the test pieces in this field of application is often very large, an individual test piece cannot be tested by means of individual image pickups. To keep the test time as short as possible, several cameras or X-ray detectors are frequently used for composing an overall image from several individual pickups.
Especially in the X-ray examination of large objects, a detector may be employed which has as large an imaging surface area as possible, which may be composed of subareas. For subsequent evaluation of the individual images using software, the individual images may be combined into an overall image. Depending on the size of the object to be examined, a large number of individual images may occur in this context which have any geometries or arrangements. One advantage associated therewith is that the image processing for composing the individual images into the overall image may become very complex and time-consuming, depending on the geometries of the images and on the number of individual images.
For X-raying very large objects, the imaging surface areas provided by the X-ray image detectors are too small in most cases. In an alternative method, the object is therefore decomposed into sub-images by displacing the detector. Displacing the detector results in problems such as precise positioning, oscillations occurring when the detector is stopped, etc. This represents a large amount of mechanical expenditure for displacing the detector, and may involve synchronization between the displacement, the image pickup and the subsequent evaluation, which eventually leads to long test times. Specifically in industrial testing of products, long test times are extremely disadvantageous because test capacities are blocked as a result of the long test times, and because of the cost resulting therefrom.
DE 103 01 941 B4 describes a camera and a method for optical recording of a screen. The camera and method described here may be employed for sensing X-ray image data, i.e. for sensing individual images. In this context, the camera comprises a camera support with an array of camera mounts to which individual optical cameras are attached, as well as an image processing means for processing digital individual images of the array of individual optical cameras so as to generate an optical pickup of the screen at a predetermined overall resolution. In this context, the image processing means performs correction of the individual images with regard to alignment inaccuracies and/or parameter fluctuations, a correction resolution being used, for correction purposes, which is higher than the overall resolution, and a dedicated correction specification being used for correcting for each individual camera. Thus, a geometric correction of the individual images is conducted before they are combined into an overall image. The geometric correction comprises aligning the individual images both in a rotational and translational manner. Once the correction has been conducted, the corrected overall image is brought to the predetermined overall resolution by combining adjacent pixels. In this manner, utilization of favorable individual cameras enables efficient, low-cost and low-artifact imaging of a large-format screen. What is problematic in this context are the image processing times, since joining the individual images may take up a lot of time, it being possible for the process times to increase disproportionately as the number of individual images increases.